Commit 996672933a has made the
freebsd-g++46 mkspec use g++-base.conf, which on its turn resets
QMAKE_CC and QMAKE_CXX to other values.
Redefine them to gcc46 and g++46, respectively (and fix the linker
values) after the inclusion of g++-unix.conf so the settings are not
lost.
Change-Id: I2d03548fdc492c5e4c4744b636b29df2cefe2acd
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@nokia.com>